9be0327a49
systemd provides two sysctl snippets, 50-coredump.conf and 50-default.conf. These enable: - Loose reverse path filtering - Source route filtering - `fq_codel` as a packet scheduler (this helps to fight bufferbloat) This also configures the kernel to pass coredumps to `systemd-coredump`. These sysctl snippets can be found in `/etc/sysctl.d/50-*.conf`, and overridden via `boot.kernel.sysctl` (which will place the parameters in `/etc/sysctl.d/60-nixos.conf`. Let's start using these, like other distros already do for quite some time, and remove those duplicate `boot.kernel.sysctl` options we previously did set. In the case of rp_filter (which systemd would set to 2 (loose)), make our overrides to "1" more explicit.
125 lines
4.5 KiB
Nix
125 lines
4.5 KiB
Nix
# A profile with most (vanilla) hardening options enabled by default,
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# potentially at the cost of features and performance.
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{ lib, pkgs, ... }:
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with lib;
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{
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meta = {
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maintainers = [ maintainers.joachifm ];
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};
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boot.kernelPackages = mkDefault pkgs.linuxPackages_hardened;
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nix.allowedUsers = mkDefault [ "@users" ];
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environment.memoryAllocator.provider = mkDefault "graphene-hardened";
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security.hideProcessInformation = mkDefault true;
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security.lockKernelModules = mkDefault true;
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security.allowUserNamespaces = mkDefault false;
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security.protectKernelImage = mkDefault true;
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security.allowSimultaneousMultithreading = mkDefault false;
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security.forcePageTableIsolation = mkDefault true;
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security.virtualisation.flushL1DataCache = mkDefault "always";
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security.apparmor.enable = mkDefault true;
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boot.kernelParams = [
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# Slab/slub sanity checks, redzoning, and poisoning
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"slub_debug=FZP"
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# Disable slab merging to make certain heap overflow attacks harder
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"slab_nomerge"
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# Overwrite free'd memory
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"page_poison=1"
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# Disable legacy virtual syscalls
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"vsyscall=none"
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# Enable page allocator randomization
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"page_alloc.shuffle=1"
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];
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boot.blacklistedKernelModules = [
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# Obscure network protocols
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"ax25"
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"netrom"
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"rose"
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];
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# Restrict ptrace() usage to processes with a pre-defined relationship
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# (e.g., parent/child)
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boot.kernel.sysctl."kernel.yama.ptrace_scope" = mkOverride 500 1;
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# Restrict access to kernel ring buffer (information leaks)
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boot.kernel.sysctl."kernel.dmesg_restrict" = mkDefault true;
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# Hide kptrs even for processes with CAP_SYSLOG
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boot.kernel.sysctl."kernel.kptr_restrict" = mkOverride 500 2;
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# Unprivileged access to bpf() has been used for privilege escalation in
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# the past
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boot.kernel.sysctl."kernel.unprivileged_bpf_disabled" = mkDefault true;
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# Disable bpf() JIT (to eliminate spray attacks)
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boot.kernel.sysctl."net.core.bpf_jit_enable" = mkDefault false;
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# ... or at least apply some hardening to it
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boot.kernel.sysctl."net.core.bpf_jit_harden" = mkDefault true;
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# Raise ASLR entropy for 64bit & 32bit, respectively.
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#
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# Note: mmap_rnd_compat_bits may not exist on 64bit.
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boot.kernel.sysctl."vm.mmap_rnd_bits" = mkDefault 32;
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boot.kernel.sysctl."vm.mmap_rnd_compat_bits" = mkDefault 16;
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# Allowing users to mmap() memory starting at virtual address 0 can turn a
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# NULL dereference bug in the kernel into code execution with elevated
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# privilege. Mitigate by enforcing a minimum base addr beyond the NULL memory
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# space. This breaks applications that require mapping the 0 page, such as
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# dosemu or running 16bit applications under wine. It also breaks older
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# versions of qemu.
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#
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# The value is taken from the KSPP recommendations (Debian uses 4096).
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boot.kernel.sysctl."vm.mmap_min_addr" = mkDefault 65536;
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# Disable ftrace debugging
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boot.kernel.sysctl."kernel.ftrace_enabled" = mkDefault false;
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# Enable strict reverse path filtering (that is, do not attempt to route
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# packets that "obviously" do not belong to the iface's network; dropped
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# packets are logged as martians).
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boot.kernel.sysctl."net.ipv4.conf.all.log_martians" = mkDefault true;
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boot.kernel.sysctl."net.ipv4.conf.all.rp_filter" = mkDefault "1";
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boot.kernel.sysctl."net.ipv4.conf.default.log_martians" = mkDefault true;
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boot.kernel.sysctl."net.ipv4.conf.default.rp_filter" = mkDefault "1";
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# Ignore broadcast ICMP (mitigate SMURF)
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boot.kernel.sysctl."net.ipv4.icmp_echo_ignore_broadcasts" = mkDefault true;
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# Ignore incoming ICMP redirects (note: default is needed to ensure that the
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# setting is applied to interfaces added after the sysctls are set)
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boot.kernel.sysctl."net.ipv4.conf.all.accept_redirects" = mkDefault false;
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boot.kernel.sysctl."net.ipv4.conf.all.secure_redirects" = mkDefault false;
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boot.kernel.sysctl."net.ipv4.conf.default.accept_redirects" = mkDefault false;
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boot.kernel.sysctl."net.ipv4.conf.default.secure_redirects" = mkDefault false;
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boot.kernel.sysctl."net.ipv6.conf.all.accept_redirects" = mkDefault false;
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boot.kernel.sysctl."net.ipv6.conf.default.accept_redirects" = mkDefault false;
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# Ignore outgoing ICMP redirects (this is ipv4 only)
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boot.kernel.sysctl."net.ipv4.conf.all.send_redirects" = mkDefault false;
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boot.kernel.sysctl."net.ipv4.conf.default.send_redirects" = mkDefault false;
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# Restrict userfaultfd syscalls to processes with the SYS_PTRACE capability
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boot.kernel.sysctl."vm.unprivileged_userfaultfd" = mkDefault false;
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}
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